In a surprisingly frank interview with the Guardian, the Hollywood actor, now winning plaudits in the Liberace biopic Behind the Candelabra, explained the background to a condition that was thought to be nearly fatal when diagnosed three years ago.

Asked whether he now regretted his years of smoking and drinking, thought to be the cause of the disease, Douglas replied: "No. Because without wanting to get too specific, this particular cancer is caused by HPV [human papillomavirus], which actually comes about from cunnilingus."

Douglas, the husband of Catherine Zeta Jones, continued: "I did worry if the stress caused by my son's incarceration didn't help trigger it. But yeah, it's a sexually transmitted disease that causes cancer. And if you have it, cunnilingus is also the best cure for it."

The actor, now 68, was diagnosed with cancer in August 2010, following many months of oral discomfort. But a series of specialists missed the tumour and instead prescribed antibiotics. Douglas then went to see a friend's doctor in Montreal who looked inside his mouth using a tongue depressor.

"I will always remember the look on his face," Douglas has previously said. "He said: 'We need a biopsy.' There was a walnut-size tumour at the base of my tongue that no other doctor had seen."

Shortly afterwards he was diagnosed with stage four cancer (stage five is death) and embarked on an intensive eight-week course of chemotherapy and radiation. He refused to use a feeding tube, despite his palate being burnt on account of the treatment, and so lost 20kg (45lb) on a liquids-only diet. "That's a rough ride. That can really take it out of you," he told the Guardian. "Plus the amount of chemo I was getting, it zaps all the good stuff too. It made me very weak."

The treatment worked and Douglas is now more than two years clear of cancer. He has check-ups every six months, he said, "and with this kind of cancer, 95% of the time it doesn't come back".

The cause of Douglas's cancer had long been assumed to be related to his tobacco habit, coupled with enthusiastic boozing. In 1992, he was hospitalised for an addiction which some at the time claimed to be sex. Douglas himself denied this and said he was in rehab for alcohol abuse. He has also spoken of recreational drug use.

HPV, the sexually transmitted virus best known as a cause of cervical and anal cancer and genital warts, is thought to be responsible for an increasing proportion of oral cancers. Some propose that changes in sexual behaviour - a rise in oral sex in particular - are responsible. Such changes might be cultural, but could also be linked to fears about the safety of penetrative sex in the wake of the discovery of Aids.

Mahesh Kumar, a consultant head and neck surgeon in London, confirms that the last decade has seen a dramatic rise in this form of cancer, particularly among younger sufferers. Recent studies of 1,316 patients with oral cancer found that 57% of them were HPV-16 positive.

"It has been established beyond reasonable doubt that the HPV type 16 is the causative agent in oropharyngeal cancer," said Kumar, who also testified to increased recovery rates among this kind of cancer sufferer. This would help explain why Douglas was given an 80% chance of survival, despite the advanced stage of his illness.

However, Kumar expressed scepticism that Douglas's cancer was caused solely by HPV, and surprise at Douglas's assertion that cunnilingus could also help cure the condition. "Maybe he thinks that more exposure to the virus will boost his immune system. But medically, that just doesn't make sense."

The GP Ann Robinson expressed interest in how confirmation of this association would affect the rollout of the HPV vaccine, which is currently only available in the UK to girls aged 12 and 13. "My main priority with diagnosing a patient with oral cancer is to get them referred as early intervention can be so crucial. Asking for a detailed sexual history would be inappropriate at that stage."

Douglas has two children, aged 10 and 12, with his second wife, Catherine Zeta Jones, as well as an older son, Cameron, from a previous marriage. In 2010, Cameron was sentenced to five years in prison for drugs possession and dealing, and a year later had his sentence extended until 2018 after he pleaded guilty to possessing drugs in prison.

Douglas won his first Oscar aged 31 for producing One Flew Over the Cuckoo's Nest, then took a second in 1987 for his performance as the ruthless capitalist Gordon Gekko in Wall Street. He won rave reviews in Cannes recently, for his portrayal of the pianist Liberace.

Later this year he will be seen alongside Morgan Freeman, Robert De Niro and Kevin Kline in the Hangover-style comedy Last Vegas. He currently has four projects in pre-production, including a dramatisation of the 1986 Reykjavik summit, in which he plays the former US president Ronald Reagan.